Shingled magnetic recording storage system improving command completion time

ABSTRACT

The disclosed technology provides a system and method that improves command completion time in a shingled magnetic recording device system. In one implementation, the system and method include receiving a write command to write data to a first track in a band in a recording medium, seeking to a first track, reducing an on-cylinder limit (OCLIM) from a default OCLIM to a reduced OCLIM by a predetermined amount on the first track, performing write operations on the first track with the reduced OCLIM, and determining if a transfer of data to the first track band in the write operations has been substantially completed. Upon determining that a transfer of data to the first track in the write operations has been substantially completed, the OCLIM is restored from a reduced OCLIM to a default OCLIM and write operations are performed on tracks adjacent to the first track.

BACKGROUND

As requirements for data storage density increase for magnetic media,cell size decreases. A commensurate decrease in the size of a writeelement is difficult because in many systems, a strong write fieldgradient is needed to shift the polarity of cells on a magnetizedmedium. As a result, writing data to smaller cells on the magnetizedmedium using the relatively larger write pole may affect thepolarization of adjacent cells (e.g., overwriting the adjacent cells).One technique for adapting the magnetic medium to utilize smaller cellswhile preventing adjacent data from being overwritten during a writeoperation is shingled magnetic recording (SMR).

SMR allows for increased areal density capability (ADC) as compared toconventional magnetic recording (CMR) but at the cost of someperformance ability. As used herein, CMR refers to a system that allowsfor random data writes to available cells anywhere on a magnetic media.In contrast to CMR systems, SMR systems are designed to utilize a writeelement with a write width that is larger than a defined track pitch. Asa result, changing a single data cell within a data track entailsre-writing a corresponding group of shingled (e.g., sequentiallyincreasing or decreasing) data tracks.

SUMMARY

The disclosed technology provides a system and method that improvescommand completion time in a shingled magnetic recording device system.In one implementation, the system and method include receiving a writecommand to write data to a first track in a band in a recording medium,seeking to a first track in the band, reducing an on-cylinder limit(OCLIM) from a default OCLIM to a reduced OCLIM by a predeterminedamount on the first track, performing write operations on the firsttrack with the reduced OCLIM, and determining if a transfer of data tothe first track band in the write operations has been substantiallycompleted. Upon determining that a transfer of data to the first trackband in the write operations has been substantially completed, the OCLIMis restored from a reduced OCLIM to a default OCLIM and write operationsare performed on tracks adjacent to the first track.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter. These andvarious other features and advantages will be apparent from a reading ofthe following Detailed Description.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a block diagram of an example data storage system.

FIG. 2 is a flowchart of example operations for reducing commandcompletion time in a shingled magnetic recording storage system.

FIG. 3 is a flowchart of example operations for reducing commandcompletion time in a shingled magnetic recording.

FIG. 4 is a block diagram of an example computer system suitable forimplementing the technology disclosed herein.

DETAILED DESCRIPTION

The present disclosure is directed to data storage systems that improvecommand completion time (CCT) by reducing adjacent track interference(ATI) in a shingled magnetic recording (SMR) drive. The disclosedtechnology includes a system and method of dynamically tightening anon-cylinder limit (OCLIM) of a disc drive in a data storage systemduring a write transfer at a starting (or first) track during a writetransfer, and restoring the OCLIM at shingled tracks adjacent to thestarting track. The OCLIM may be defined as the off-track limit. Adefault value of OCLIM is determined during storage drive design. When awriter position from the track center (position error signals) isgreater than an OCLIM, the writing operation may be stopped. In someimplementations, the range of OCLIM is approximately 7-14% track pitch.In some implementations, the unit of OCLIM may be a minch. For example,0.1 minch.

An SMR drive is a storage device that uses bands of overlapping tracksto increase storage density. In SMR, a new track may be written thatpartially overlaps a previously written track, creating a shingledaspect to the tracks. SMR leverages the fact that a width of a read headis typically narrower than the width of a write head. The storagedensity of an SMR drive is increased over conventional drives becausethe previously written tracks are thinner, allowing for higher trackdensity. In an SMR drive, a set of bands of overlapping tracks may beseparated by an isolation space, which serves to reduce the number oftracks that need to be rewritten when a shingled track is rewritten.

The technology disclosed herein can be used with various data storagedevices. Examples of such data storage devices include hard disc drives,solid state hybrid drives, solid state media such as NAND, NVRAM,Resistive RAM (ReRAM), Magnetic RAM (MRAM), Phase Change Memory (PCM),and other memory technologies.

In the following description, reference is made to the accompanyingdrawing that forms a part hereof and in which are shown by way ofillustration at least one specific embodiment. In the drawing, likereference numerals are used throughout several figures to refer tosimilar components. In some instances, a reference numeral may have anassociated sub-label consisting of a lower-case letter to denote one ofmultiple similar components. When reference is made to a referencenumeral without specification of a sub-label, the reference is intendedto refer to all such multiple similar components.

FIG. 1 illustrates a block diagram of an example data storage system100, showing various functional components used to control the operationof a data storage device 110 (e.g., an SMR HDD, an SMR SSHD, an objectstorage device, etc.).

The data storage system 100 includes a computing or computing device 102(e.g., a computer, a mobile device, the internet, etc.) operablyconnected to the data storage device 110, each of the computing device102 and the data storage device 110 communicating with each other.

A processor 104 is located in the computing device 102. The processor104 sends one or more read or write commands to a storage devicecontroller 112 for execution. As control communication paths areprovided between the computing device 102 and the storage devicecontroller 112, the storage device controller 112 provides communicationand control for the data storage device 110.

Storage media 114 located in the data storage device 110 may be one ormore of a variety of tangible media (excluding carrier waves andcommunication signals), including hard disk drives and solid statehybrid drives, store data on magnetic media, as well as optical media,solid state media such as NAND, NVRAM, Resistive RAM (ReRAM), MagneticRAM (MRAM), Phase Change Memory (PCM), and other advanced and staidmemory technologies.

The data storage device 110 further includes a non-volatile cache 116that is either a storage area on the storage media 114 or anothernon-volatile memory accessible by the data storage device 110. In thedepicted system 100, the cache 116 is a storage area on the storagemedia 114.

A band 120 of shingled tracks (e.g., track 130) may also be located inthe storage media 114. In FIG. 1, the shingled tracks 130 are located inthe band 120 are shown. An implementation of the shingled tracks 130 isarranged such that when data is written to one of the shingled tracks130 (except for the last data track), a writing operation affects dataon an adjacent track in a down-track direction.

On a band-based SMR drive, partial band writing or writing from themiddle of a band may introduce more ATI due to a higher track per inch(TPI). In shingled recording, only one side of an adjacent track may beaffected. In the case of a direct off-line scan (DOS) operation, abackground ATI repair scheme based on write count, a scan of a datatrack after a particular number of data writes to an immediatelyadjacent or near data track. A DOS operation records the write count tophysical tracks and starts a background scan/refresh operation torecover the tracks that have been encroached by adjacent trackinterference (ATI). A DOS operation measures the track degradation bywrite count. The higher the write count, the more encroachment isdetermined. In SMR implementations, a track repair process may read andrewrite full/partial band range even if only one track requires repair,which may introduce a much longer CCT and significant processingoverhead. A DOS operation may impact user command completion time. Incertain disc aggressive applications, such as surveillance or multiplevideo streaming, a long CCT can interrupt the media streaming and userexperience may be affected. In surveillance, for example, security gapsmay arise. Tightening OCLIM can reduce ATI, thereby reducing DOSactivity. However, extra disc retry can be introduced if write OCLIM istightening, which eventually affects a drive throughput.

In band basis recording, only a starting track (e.g., track 134) willcreate unrecoverable disk error (UDE) on an adjacent track (e.g., track132) in front of it. The following tracks (e.g., tracks 130) will notaffected by ATI because the following tracks are to be overwritten orrewritten through band updating operation. The disclosed technologyincludes tightening an OCLIM at the starting track 134 only during bandupdating, so that the ATI can be mitigated, and the majority of discwrite will not impacted. In some implementations, the OCLIM may betightened by approximately 2% at the first track 134 of transfer,resulting in approximately 50% reduction of background DOS work, whichis visible improvement for CCT.

The disclosed disc write scheme dynamically tightens an OCLIM throughservo command before starting transfer on the first track 134, byreducing a default OCLIM (e.g., default OCLIM 108) to a reduced OCLIM(e.g., reduced OCLIM 106), and then restores OCLIM to a normal limit(default OCLIM 108) before transferring on the following tracks (e.g.,track 132, tracks 130). As a result, the ATI risk in an SMR drive can bemitigated and also throughput at a high level. With a reduced DOSworkload, long CCT occurrence will be reduced, which will eventuallyimprove overall user experience, particularly in multimedia streamingand surveillance.

FIG. 2 is a flowchart of example operations 200 for reducing commandcompletion time in a shingled magnetic recording storage system. Anoperation 202 receives a write command for a storage controller to writedata to a first track in a band in a recording medium. In someimplementations, the recording medium is an SMR medium.

An operation 204 seeks to the first track in the band of the recordingmedium. An operation 206 reduces an OCLIM from a default OCLIM to areduced OCLIM by a predetermined amount on the first track via servocommand. The predetermined amount may be a predefined percentage of thenominal trach pitch for the disc drive. For example, the predeterminedamount may be approximately 2%.

An operation 208 performs write operations on the first track with thereduced OCLIM. An operation 210 determines if a transfer of data to thefirst track in the write operations has been substantially completed. Ifoperation 210 determines that a transfer of data to the first track inthe write operations has been substantially completed, an operation 214restores the OCLIM from a reduced OCLIM to a default OCLIM. An operation216 performs write operations on tracks adjacent to the first track.

If operation 210 determines that a transfer of data to the first trackin the write operations has not been completed, an operation 212performs a retry operation until the transfer of data to the first trackhas been completed. The operation 212 performs the retry operation, andoperation 210 will occur again and determine if a transfer of data tothe first track in the write operations has been substantiallycompleted. If operation 210 determines the transfer of data to the firsttrack in the write operations has not been substantially completed, thenoperation 212, and operation 210 occur again until write operations havebeen substantially completed. Once write operations have beensubstantially completed, operations 214 and 216 may occur, as describedabove.

FIG. 3 is a flowchart of example operations 300 for reducing commandcompletion time in a shingled magnetic recording storage system. Anoperation 302 receives a write command to write data to a first track ina band in a recording medium. An operation 304 seeks to the first trackin the band. An operation 306 reduces an OCLIM from a default OCLIM to areduced OCLIM by 2% on the first track via a servo command. An operation208 performs write operations on the first track with the reduced OCLIM.As a result, CCT is improved in an SMR drive by reduction of backgroundDOS media repair activities, the SMR drive lifespan is improved due toreduction of media read/write, and user experience is improved (e.g.,non-interrupted media streaming).

FIG. 4 discloses a block diagram of a computer system 400 suitable forimplementing operations for reducing command completion time in ashingled magnetic recording storage system. Computer system 400 iscapable of executing a computer program product embodied in a tangiblecomputer-readable storage medium to execute a computer process. Thetangible computer-readable storage medium is not embodied in acarrier-wave or other signal. Data and program files may be input tocomputer system 400, which reads the files and executes the programstherein using one or more processors. Some of the elements of a computersystem are shown in FIG. 4, where a processor 402 is shown having aninput/output (I/O) section 404, a Central Processing Unit (CPU) 406, anda memory 408. There may be one or more processors 402, such thatprocessor 402 of system 400 has a single central-processing unit or aplurality of processing units. System 400 further incudes a controller,not shown in FIG. 4, configured to designate a plurality ofnon-contiguous storage areas on the storage media as media scratch pads;the controller may be software, firmware, or a combination thereof.System 400 may be a conventional computer, a distributed computer, orany other type of computer. The described technology is optionallyimplemented in software loaded in memory 408, a disc storage unit 412,or removable memory 418.

In an example implementation, the disclosed process of reducing CCT inSMR may be embodied by instructions stored in memory 408 and/or discstorage unit 412 and executed by CPU 406. Further, local computingsystem, remote data sources and/or services, and other associated logicrepresent firmware, hardware, and/or software which may be configured toadaptively distribute workload tasks to improve system performance. Theuse of the media scratch pad may be implemented using a general purposecomputer and specialized software (such as a server executing servicesoftware), and a special purpose computing system and specializedsoftware (such as a mobile device or network appliance executing servicesoftware), or other computing configurations. In addition, program data,such as dynamic allocation threshold requirements and other informationmay be stored in memory 408 and/or disc storage unit 412 and executed byprocessor 402.

The implementations of the invention described herein are implemented aslogical steps in one or more computer systems. The logical operations ofthe present invention are implemented (1) as a sequence ofprocessor-implemented steps executing in one or more computer systemsand (2) as interconnected machine or circuit modules within one or morecomputer systems. The implementation is a matter of choice, dependent onthe performance requirements of the computer system implementing theinvention. Accordingly, the logical operations making up the embodimentsof the invention described herein are referred to variously asoperations, steps, objects, or modules. Furthermore, it should beunderstood that logical operations may be performed in any order, addingand omitting as desired, unless explicitly claimed otherwise or aspecific order is inherently necessitated by the claim language.

The above specification, examples, and data provide a completedescription of the structure and use of exemplary embodiments of theinvention. The above description provides specific embodiments. It is tobe understood that other embodiments are contemplated and may be madewithout departing from the scope or spirit of the present disclosure.The above detailed description, therefore, is not to be taken in alimiting sense. While the present disclosure is not so limited, anappreciation of various aspects of the disclosure will be gained througha discussion of the examples provided.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties are to be understood as being modifiedby the term “about.” Accordingly, unless indicated to the contrary, thenumerical parameters set forth are approximations that can varydepending upon the desired properties sought to be obtained by thoseskilled in the art utilizing the teachings disclosed herein.

As used herein, the singular forms “a”, “an”, and “the” encompassembodiments having plural referents, unless the content clearly dictatesotherwise. As used in this specification and the appended claims, theterm “or” is generally employed in its sense including “and/or” unlessthe content clearly dictates otherwise.

Spatially related terms, including but not limited to, “lower”, “upper”,“beneath”, “below”, “above”, “on top”, etc., if used herein, areutilized for ease of description to describe spatial relationships of anelement(s) to another. Such spatially related terms encompass differentorientations of the device in addition to the particular orientationsdepicted in the figures and described herein. For example, if astructure depicted in the figures is turned over or flipped over,portions previously described as below or beneath other elements wouldthen be above or over those other elements.

Since many embodiments of the invention can be made without departingfrom the spirit and scope of the invention, the invention resides in theclaims hereinafter appended. Furthermore, structural features of thedifferent embodiments may be combined in yet another embodiment withoutdeparting from the recited claims.

What is claimed is:
 1. A method comprising: receiving a write command towrite data to a first track in a band in a recording medium; seeking tothe first track in the band; reducing an on-cylinder limit (OCLIM) froma default OCLIM to a reduced OCLIM on the first track in the band by apredetermined amount; and performing write operations on the first trackwith the reduced OCLIM.
 2. The method of claim 1, wherein thepredetermined amount is approximately 2%.
 3. The method of claim 1,wherein the recording medium is shingled magnetic recording medium. 4.The method of claim 1, further comprising: determining if a transfer ofdata to the first track in the write operations has been substantiallycompleted.
 5. The method of claim 4, further comprising: restoring theOCLIM from a reduced OCLIM to a default OCLIM responsive to determiningthat a transfer of data to the first track band in the write operationshas been substantially completed; and performing write operations ontracks adjacent to the first track.
 6. The method of claim 4, furthercomprising: performing a retry operation responsive to determining atransfer of data to the first track in the write operations has not beencompleted; reducing the OCLIM from a default limit to a reduced limit;and determining if a transfer of data to the first track in the writeoperations has been substantially completed.
 7. The method of claim 6,further comprising: restoring the OCLIM from the reduced limit to thedefault limit responsive to determining a transfer of data to the firsttrack band in the write operations has been substantially completed; andperforming a write operation on tracks adjacent to the first track.
 8. Astorage device system, comprising: a storage controller configured to:receive a write command to write data to a first track in a band in arecording medium; seek to a first track in the band; reduce anon-cylinder limit (OCLIM) from a default OCLIM to a reduced OCLIM on thefirst track in the band by a predetermined amount; and perform writeoperations on the first track in the band with the reduced OCLIM.
 9. Thestorage device system of claim 8, wherein the recording medium isshingled magnetic recording medium.
 10. The storage device system ofclaim 8, wherein the predetermined amount is approximately 2%.
 11. Thestorage device system of claim 8, wherein the storage controller isfurther configured to: determine if a transfer of data to the firsttrack in the band in the write operations has been substantiallycompleted.
 12. The storage device system of claim 11, wherein thestorage controller is further configured to: restore the OCLIM from areduced OCLIM to a default OCLIM responsive to determining that atransfer of data to the first track in the band in the write operationshas been substantially completed; and perform write operations on tracksadjacent to the first track in the band.
 13. The storage device systemof claim 8, wherein the storage controller is further configured to:perform a retry operation responsive to determining a transfer of datato the first track in the band in the write operations has not beencompleted; reduce the OCLIM to a reduced limit; and determine if atransfer of data to the first track in the band in the write operationshas been substantially completed.
 14. The storage device system of claim13, wherein the storage controller is further configured to: restore thedefault OCLIM on tracks adjacent to the first track in the bandresponsive to determining that a transfer of data to the first track inthe band in the write operations has been substantially completed; andperform a write operation on tracks adjacent to the first track in theband.
 15. One or more non-transitory computer-readable storage mediaencoding computer-executable instructions for executing on a computersystem a computer process, the computer process comprising: receiving awrite command to write data to a first track in a band in a recordingmedium; seeking to a first track in the band; reducing an on-cylinderlimit (OCLIM) from a default OCLIM to a reduced OCLIM on the first trackin the band by a predetermined amount; and performing write operationson the first track in the band with the reduced OCLIM.
 16. The one ormore non-transitory computer-readable storage media of claim 15, furthercomprising: determining if a transfer of data to the first track in theband in the write operations has been substantially completed.
 17. Theone or more non-transitory computer-readable storage media of claim 16,further comprising: restoring the OCLIM from a reduced OCLIM to adefault OCLIM responsive to determining that a transfer of data to thefirst track in the band in the write operations has been substantiallycompleted; and performing write operations on tracks adjacent to thefirst track in the band.
 18. The one or more non-transitorycomputer-readable storage media of claim 16, further comprising:performing a retry operation responsive to determining a transfer ofdata to the first track in the band in the write operations has not beencompleted; reducing the OCLIM from a default limit to a reduced limit;and determining if a transfer of data to the first track in the band inthe write operations has been substantially completed.
 19. The one ormore non-transitory computer-readable storage media of claim 18, furthercomprising: restoring the OCLIM from a reduced limit to a default limitresponsive to determining a transfer of data to the first track in theband in the write operations has been substantially completed; andperforming a write operation on tracks adjacent to the first track inthe band.
 20. The one or more non-transitory computer-readable storagemedia of claim 15, wherein the recording medium is shingled magneticrecording medium.